1. Field of the Invention
The invention relates to a device for exposing the outside peripheral area of a semiconductor wafer having a V-shaped notch in its periphery in order to remove a photoresist which has been applied to the surface of the semiconductor wafer.
2. Description of the Related Art
Conventionally, a device for exposure of a peripheral area of a wafer is as shown in FIG. 13(a). During exposure, an area S irradiated with exposure light is moved such that it follows the edge E of the wafer W, and the peripheral area of the wafer W, to which a photoresist R has been applied, is exposed with a given exposure width A.
In the conventional device for exposing a peripheral area, the peripheral area of the wafer W is exposed such that the edge E of the wafer W is always captured. However, in the outside peripheral area a V-shaped notch N is formed. When the wafer W is exposed, the area S irradiated with the exposure light moves in a V-shape in the area of the notch N. As a result, a phenomenon was encountered in that an area UE which is located within the interior of the wafer W and which need not be exposed is also exposed, as shown in FIG. 13(b). Therefore in the vicinity of the above described area UE there can not be an area in which a semiconductor component (a circuit pattern or the like) is formed; this is an impediment to an increase in productivity for semiconductor components. Therefore, the applicant has already proposed, in JP 2001-151037, a device for exposing the peripheral area in which the irradiated area is prevented from moving in a V-shape in the notch area of the wafer, i.e., the area located inside the V-shaped edge area of the wafer which need not be exposed is prevented from being exposed.
Exposure of the peripheral wafer area in the device described in JP 2001-151037 is illustrated in FIGS. 14(a) to 14(d).
In that device for exposing a peripheral area, the exposure light irradiation part which exposes the peripheral area of the wafer is located integrally with a means for wafer edge determination, which follows the edge E of the wafer W and moves in the direction which is essentially perpendicular to a tangent of the edge of the wafer W. The exposure light emitted from the exposure light irradiation part has an irradiation area S which moves in the same direction and by the same amount as the means for wafer edge determination. In this way the peripheral area of the wafer edge E is exposed.
Furthermore, there is a notch determination means, upstream of the wafer edge determination means, for determining the notch of the wafer. In the following, the term xe2x80x9cupstreamxe2x80x9d is defined as the peripheral area of the wafer which moves toward the means for wafer edge determination when the wafer is turned, and the term xe2x80x9cdownstreamxe2x80x9d is defined as the peripheral wafer area which moves away from the means for wafer edge determination.
The notch determination means described above is arranged integrally with the means for wafer edge determination and the exposure light irradiation part, and is synchronized with the means for wafer edge determination and is moved in the direction essentially perpendicular to the tangent of the edge of the wafer W.
A condition is described below in which the peripheral area of a wafer has an outside peripheral area provided with a notch and to which a photoresist has been applied. The photoresist is exposed by the above described device to expose a peripheral area by determining the edge of this wafer. In FIGS. 14(a) to 14(d) the notch area of the wafer is shown enlarged.
The wafer W which has been placed on the treatment stage is turned clockwise, as shown in FIGS. 14(a) to 14(d). The means for wafer edge determination determines the edge E of the wafer W at the position. The area S irradiated with the exposure light from the exposure light irradiation part is located on the surface of the wafer W essentially at the same location as the above described position. The notch determination means upstream of the wafer W, i.e., at position , determines the edge E of the wafer W.
The four situations encountered during exposure will now be described.
(1) When the edge area except for the notch of the wafer is determined by the notch determination means, as is shown in FIG. 14(a):
The means for wafer edge determination follows the wafer edge and moves in the direction essentially perpendicular to the tangent of the edge of the wafer W. The exposure light irradiation part located integrally with it moves together with the wafer edge determination means. The area S irradiated with the exposure light from the exposure light irradiation part therefore follows the wafer edge E and moves. Thus, as shown in FIG. 14(a), the peripheral wafer area is exposed.
(2) When the notch determination means has reached the start of the notch of the wafer, as shown in FIG. 14(b):
When the wafer W turns clockwise and the start Ns of the notch N of the wafer W reaches the determination position  of the notch determination means, the notch determination means outputs an ON signal. In this way, a controller (not shown) computes the time T1 at which the area S irradiated with the exposure light reaches the start Ns of the notch N based on the rotational speed of the wafer W and the distance between the determination position  of the notch determination means and the position of the wafer edge determination means (in this example 5 mm).
(3) When the time T1 has lapsed after the notch determination means has reached the start Ns of the notch, as was shown in FIG. 14(c):
When time T1 elapses after the notch determination means has reached the start Ns of the notch N, the area S irradiated with the exposure light reaches the start Ns of the notch N. In this way, the controller stops the operation in which the wafer edge determination means follows the edge E of the wafer W. Therefore, the wafer edge determination means and the area S irradiated with the exposure light do not follow the notch N, but move along the tangent of the edge E of the area directly in front of the notch N of the wafer W.
The above described controller computes the time T2 at which operation of the wafer edge determination means follows the edge E of the wafer W is restarted after stopping. For example, based on the gap dimensions, the notch N is determined and based on the rotational speed of the wafer W, the time T2 at which the area S travels from the start Ns of the notch N to the end Ne of the notch N is determined.
(4) When time T2 has elapsed, as shown in FIG. 14(d):
When time T2 elapses after the area S has reached the start of the notch Ns, the area S reaches the end Ne of the notch N. The controller then restarts operation in which the wafer edge determination means follows the edge E of the wafer W. In this way the means for wafer edge determination moves such that it follows the wafer edge E. As was shown above using FIG. 14(a), the area S irradiated with the exposure light which has been emitted from the exposure light irradiation part moves in such a way that it follows the wafer edge E. Thus, as shown in FIG. 14(d), the peripheral wafer area is exposed.
By the above described process, the tracking operation of the means for wafer edge determination is stopped after a given time has lapsed, i.e., after it has received the signal which indicates the notch start Ns. The tracking operation of the wafer edge determination means is restarted, after a further given time T2 has elapsed, i.e. when the area S reaches the end Ne of the notch N. By this method the irradiation area in the notch area of the wafer is prevented from following the notch and from moving in a V-shape, and the area located inside the wafer, which need not be exposed, is prevented from being exposed.
In the above described device for exposure of a peripheral area the wafer, the edge determination means moves in the radial direction of the wafer when exposure of the peripheral area starts. When the wafer edge determination means determines the wafer edge, the means for wafer edge determination stops motion in the radial direction of the wafer. At the position at which the edge could be determined, irradiation with the exposure light is begun and thus exposure of the peripheral area is started.
However, if normally a notched wafer W is placed on the rotary treatment stage of the device for exposing the peripheral area, the position of the notch N (i.e. in which direction the notch is to be placed) is not fixed.
When exposure starts, the notch determination means therefore cannot determine, before the means for wafer edge determination, the starting position of the notch when the means for wafer edge determination or the notch determination means is located in the vicinity of the notch N in the position at which the wafer edge was initially determined, as is described below in (a) to (c):
(a) when the position of the means for wafer edge determination and the position of the notch agree with one another;
(b) when the notch is between the notch determination means and the means for wafer edge determination;
(c) when the position of the notch determination means and the position of the notch agree with one another.
Therefore, stop control of the tracking operation of the means for wafer edge determination cannot be carried out. That is, the above described peripheral area exposure in which there is no conformity with the notch cannot be carried out, i.e. in which the notch is ignored (also called xe2x80x9cnotch disregardxe2x80x9d below).
In the above described situations, the position at which the means for wafer edge determination determines the wafer edge, and the position which is irradiated with the exposure light which exposes the peripheral area of the wafer agree with one another, as was described above.
Also as was described above, in the conventional peripheral area exposure the phenomenon occurs, in the above described cases (a) to (c), where peripheral area exposure in which the notch is ignored cannot be done, and the area located within the wafer (which does not need to be exposed) is also exposed.
The invention strives to eliminate the above described disadvantages. The object of the invention is to provide a device for exposing the peripheral area when in the above described cases (a) to (c), that is, those situations in which the means for wafer edge determination or the notch determination means are located in the vicinity of the notch, peripheral area exposure can be done in which the notch is ignored and in which it is possible to prevent the area within the wafer from being exposed.
The object is achieved by the invention as follows:
After determining the wafer edge by the means for wafer edge determination, the exposure light is not emitted immediately, but the wafer is turned by a given amount, and afterwards exposure is started. If, during the above described rotation, the output signal of the above described notch determination means has changed, based on the timing of the initial change of the notch determination means, the starting position of the notch can be detected. Therefore, at the exposure start position which has been established beforehand according to the change state of this output signal, irradiation with wafer exposure light is started and the above described control is effected in which the notch is disregarded when the irradiation area has reached the notch starting position.
The above described given amount of rotation must be at least larger than the distance (D1) which corresponds to the distance between the means for wafer edge determination and the notch determination means.
The above described measure makes it possible, in the states (a) to (c) above, to also carry out peripheral exposure in the manner to be described below, in which the notch is ignored. Furthermore, the above described measures prevent the area which is located within the wafer (and which need not be exposed) from being exposed.
(1) When the position of the means for wafer edge determination and the position of the notch agree with one another, as was described in (a).
By turning the wafer by the means for wafer edge determination by a given amount of (D1+xcex1) (here xe2x80x9cxcex1xe2x80x9d denotes the deviation which is determined to balance the mounting and control errors by experimentation or the like) from the position at which the wafer edge has been determined, the means for wafer edge determination diverges from the notch. From there exposure is begun. After starting exposure, when the wafer has been turned essentially once, the notch is determined by the notch determination means. Therefore motion of the exposure light irradiation part is stopped and exposure is done such that it does not follow the notch area, as was described above.
(2) When the notch is located between the notch determination means and the means for wafer edge determination, as was described above in (b).
By rotation of the wafer by a given amount of (D1+xcex1) the notch passes through the position of the means for wafer edge determination, as in case (1). The means for wafer edge determination reaches a position away from the notch. From there exposure is begun. After starting exposure, when the wafer has been turned essentially once, the notch is determined by the notch determination means. Therefore motion of the exposure light irradiation part is stopped and exposure is carried out such that it does not follow the notch area, as was described above.
(3) When the position of the notch determination means and the position of the notch agree with one another, as was described in (c).
In this case, at the instant at which the means for wafer edge determination has determined the wafer edge, the notch determination means outputs a notch determination signal. But since it is unknown where the starting position of the notch is located, the timing for stopping motion of the exposure light irradiation part is unclear.
Therefore, as was described above, the wafer is turned by the given amount (D1+xcex1) and afterwards it is turned further at least by an amount (D2+xcex1) which corresponds to the width of the notch. In this way the notch passes through the position of the means for wafer edge determination and the means for wafer edge determination reaches a position outside of the notch. Therefore, proceeding from this position exposure begins. After starting exposure, when the wafer has turned essentially once, the notch is determined by the notch determination means. Therefore motion of the exposure light irradiation part is stopped and notch disregard exposure is carried out, as was described above.
In this case, during rotation of the wafer by the above described amount of (D1+xcex1), the output of the notch determination means is shifted into the OFF state. Based on the timing, the notch width and the like, the starting position of the notch can be detected. Therefore, instead of the above described rotation of the wafer, turned at least by the amount of (D2+xcex1), which corresponds to the width of the notch, the above described notch disregard control can begin when the area irradiated with the exposure light is reached for the notch start position which has been determined in the above described manner.
The above described states (a) to (c) are conditions in the determination of the wafer edge. But there are also situations in which the above described states (a) to (c) are obtained, at the instant of rotation of the wafer by the given amount. In this case however, the output state of the notch determination means changes by a given amount during rotation of the wafer. Based on this output change, the relative position of the area irradiated with the exposure light to the notch can be determined. Therefore, by fixing the instant of the start of exposure based on the position of the area irradiated with the exposure light relative to the notch, which position has been determined in the above described manner, and by the above described notch disregard control the disadvantage that the area which is located within the wafer (and which need not be exposed) is not exposed.
Specifically, when starting exposure the procedure is as follows:
(A) If during rotation of the wafer by the given amount of (D1+xcex1) after determining the wafer edge the output of the notch determination means does not change.
In this case there are the following cases:
(1) Case in which the notch area is not involved at all.
(2) Case in which the notch is between the notch determination means and the means for wafer edge determination when the wafer edge is being determined.
(3) Case in which the position of the means for wafer edge determination and the position of the notch agree with one another when the wafer edge is determined.
In the above described case (1) the notch area is not involved at all. Therefore no problem arises even if directly after rotation of the wafer by the above described amount of (D1+xcex1) exposure is started.
The above described cases (2) and (3) relate to the cases of the above described states (a) and (b). Therefore no problem arises even if after rotation of the wafer by the above described amount of (D1+xcex1) exposure is started.
(B) If during rotation of the wafer by the give amount of (D1+xcex1) after determination of the wafer edge the output of the notch determination means is changed.
In this case, based on the output of the notch determination means, the relative distance between the irradiation area and the notch starting position can be determined. It is therefore possible to carry out the above described notch disregard control even if exposure starts immediately when the output is generated by the notch determination means. Thus the disadvantage of exposing the area located within the wafer can be avoided.
In practice, considering the simplification of the control sequence, the instant for the exposure start can be set in the manner described below.
(1) As in the above described case A, after rotation of the wafer by the given amount of (D1+xcex1), exposure is begun. If during the above described rotation, the notch determination means produces an output, the relative distance between the irradiation area and the notch starting position is determined based on this output. When the irradiation area reaches the notch starting position, the above described notch disregard control is carried out.
In this case, besides the above described case (3) (case in which the position of the notch determination means and the position of the notch agree with one another) after rotation of the wafer by the given amount of (D1+xcex1), exposure is begun. The control sequence is therefore relatively simple.
(2) As in the above described case A, after rotation of the wafer by the given amount of (D1+xcex1) the wafer is additionally rotated by the above described amount of (D2+xcex1) which corresponds to the width of the notch, and afterwards exposure is begun. When the irradiation area reaches the notch starting position, the above described notch disregard control is carried out.
In this case exposure is begun after the wafer has been rotated in all cases by the given amount of (D1+xcex1) and by the above described amount of (D2+xcex1) which corresponds to the width of the notch. The control sequence is therefore especially simple. The instant at which exposure is begun is however delayed, by which the throughput is reduced.
(3) When the output signal of the notch determination means changes, exposure is begun immediately. This is the case in which exposure begins immediately when an output is generated by the above described notch determination means. Compared to the above described cases (1) and (2), an earlier instant for the start of exposure can be taken, increasing the throughput. The control sequence becomes more complex, however, when compared to the above described cases (1) and (2).
The invention is further described below using several embodiments shown in the drawings.